The Labour Party had been pushed into third place in 1983, taking 22% of the vote.[1] They also re-stood their candidate from the previous year, Sally Thomas, a supporter of unilateral nuclear disarmament. As Portsmouth South was the headquarters of the Royal Navy, this was a significant issue in the campaign.[3]

Three other candidates had stood in the general election,[1] and two of these stood in the by-election: Gordon Knight of the far rightNational Front, and Alan Evens who stood as "Liberal for Unilateral Nuclear Disarmament", while four new candidate completed the field. Terry Mitchell stood for the Ecology Party, Thomas Layton stood as "Spare the Earth - Ecology", Anthony Andrews stood as an independent with the slogan "Vote Education: Save Schools & Colleges", and Pete Smith stood for the New National Party.[2]